Tin-based catalysts, the preparation thereof, and fuel cells using the same

ABSTRACT

A composition comprised of a tin (Sn) or lead (Pb) film, wherein the film is coated by a shell, wherein the shell: (a) is comprised of an active metal, and (b) is characterized by a thickness of less than 50 nm, is discloses herein. Further disclosed herein is the use of the composition for the oxidation of e.g., methanol, ethanol, formic acid, formaldehyde, dimethyl ether, methyl formate, and glucose.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. Divisional Application of U.S. patentapplication Ser. No. 16/327,951, filed on Feb. 25, 2016, which is aNational Phase of PCT Patent Application No. PCT/IL2017/050950 titled“TIN-BASED CATALYSTS, THE PREPARATION THEREOF, AND FUEL CELLS USING THESAME” having International filing date of Aug. 27, 2017, which claimsthe benefit of priority from U.S. Provisional Patent Application No.62/379,813, filed on Aug. 26, 2016. The contents of the aboveapplications are all incorporated by reference as if fully set forthherein in their entirety.

FIELD OF INVENTION

The present invention, in some embodiments thereof, relates toplatinum-tin based catalysts.

BACKGROUND OF THE INVENTION

A fuel cell converts chemical energy directly into electric energy bysupplying a fuel and an oxidant to two electrically-connected electrodesand thus causing electrochemical oxidation of the fuel.

Noble metal catalysts such as a platinum catalyst and a platinum alloycatalyst have been used as the catalyst of the anode and cathodeelectrodes of a fuel cell. However, noble metal catalysts are scarceresources and it is expensive to use them for large-scale commercialproduction of fuel cells.

In noble metal catalyst particles, catalytic reaction occurs on thesurface of the particles only and the inside of the particles seldomparticipates in catalytic reaction. Therefore, the catalytic activityper unit mass of a noble metal catalyst particle is not always high.

Catalyst particles having a structure such that a core particle iscovered with an outermost layer, that is, a so-called core-shellstructure, can increase the catalytic activity per unit mass of a noblemetal catalyst. Catalyst particles having a core-shell structure cansecure catalytic activity and cost reduction by using a material withexcellent catalytic activity as the outermost layer together withinexpensive material which does not directly participate in catalyticreaction as the core particle.

SUMMARY OF THE INVENTION

According to an aspect of some embodiments of the present invention,there is provided a composition comprising film comprising an elementselected from the group consisting of: tin (Sn), lead (Pb), or acombination thereof, wherein the Sn film is coated by a shell, whereinthe shell: (a) comprises an active metal, and (b) is characterized by athickness of less than 50 nm. In some embodiments, the thickness is inthe range of 2 nm to 10 nm.

In some embodiments, the active metal is selected from the groupconsisting of: platinum (Pt), palladium (Pd), or an alloy thereof.

In some embodiments, the shell further comprises a material selectedfrom the group consisting of Sn, ruthenium (Ru), selenium (Se), or anycombination thereof.

According to an aspect of some embodiments of the present invention,there is provided a composition comprising a film comprising an elementselected from the group consisting of: tin (Sn), lead (Pb), or acombination thereof, a material comprising one or more active metalnanoparticles (NPs), and a substrate, wherein the film is: (a) depositedon at least one surface of the substrate, and (b) coated by the materialcomprising the one or more active metal NPs.

In some embodiments, a plurality of the nanoparticles forms a shell onthe Sn film, the shell being characterized by a thickness of less than10 nm.

In some embodiments, the Sn film is in the form of dendritic structurehaving a stem and branches.

In some embodiments, the stem and branches are characterized by a ratioof 1:1 to 5:1, respectively.

According to an aspect of some embodiments of the present invention,there is provided a fuel cell having an electrocatalyst comprising thedisclosed composition in an embodiment thereof.

In some embodiments, the electrocatalyst is anode.

In some embodiments, the electrocatalyst is characterized by anelectrochemically active surface area of at least 75 m²g⁻¹.

According to an aspect of some embodiments of the present invention,there is provided a process for manufacturing a catalyst comprising asubstrate having attached thereon an Sn or Pb film, wherein: (a) thefilm is coated by one or more active metal NPs and optionally an elementselected from the group consisting of Sn, ruthenium (Ru), selenium (Se),or any combination thereof, and (b) the substrate comprises one or morematerials selected from carbon (e.g., carbon black), a metal oxide, apolymer, or any combination thereof, the process comprising the stepsof: (i) electrodepositing the Sn film on the substrate; and (ii) platinga material comprising the active metal NPs and optionally the M on theSn film, thereby obtaining the catalyst.

In some embodiments, step (ii) is performed by electroplating orelectroless plating.

According to an aspect of some embodiments of the present invention,there is provided a use of the disclosed composition, for the oxidationof a material selected from methanol, ethanol, formic acid,formaldehyde, dimethyl ether, methyl formate, and glucose.

Further embodiments and the full scope of applicability of the presentinvention will become apparent from the detailed description givenhereinafter. However, it should be understood that the detaileddescription and specific examples, while indicating preferredembodiments of the invention, are given by way of illustration only,since various changes and modifications within the spirit and scope ofthe invention will become apparent to those skilled in the art from thisdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

Some embodiments of the invention are herein described, by way ofexample only, with reference to the accompanying drawings. With specificreference now to the drawings in detail, it is stressed that theparticulars shown are by way of example and for purposes of illustrativediscussion of embodiments of the invention. In this regard, thedescription taken with the drawings makes apparent to those skilled inthe art how embodiments of the invention may be practiced.

In the drawings:

FIGS. 1A-B present scanning electron microscopic (SEM) image of tindendrites formed by electrodeposition at different magnification (FIG.1A) 50 μm and 5 μm (FIG. 1B);

FIGS. 2A-B present high resolution (HR) SEM image of PtSn@Sn catalyst(FIG. 2A; bar is 100 nm; numbers in the image depict the size of theparticles as described below) and energy-dispersive X-ray spectroscopy(EDX) of Pt@Sn catalyst (Red: Platinum, Blue: Sn, Green: Oxygen; FIG.2B, bar is 300 nm);

FIGS. 3A-B present HRSEM image of Pt@Sn catalyst (FIG. 3A, bar is 500nm; numbers in the image depict the size of the particle as describedbelow), and EDX of PtSn@Sn catalyst (Red: Platinum, Blue: Sn, Green:Oxygen; FIG. 3B);

FIG. 4 presents cyclic voltammetry of electrodes in supportingelectrolyte (0.5M H₂SO₄).

FIG. 5 presents cyclic voltammetry of oxidation of formic acid (FA) onPt@Sn (lower graph) and PtSn@Sn (upper graph) catalyst in 0.5 M H₂SO₄and 1.0 HCOOH;

FIG. 6 presents cyclic voltammetry of oxidation of methyl formate (MF)on Pt@Sn (lower graph) and PtSn@Sn (upper graph) catalyst in 0.5 HCOOCH₃and 1.0 M H₂SO₄;

FIG. 7 presents cyclic voltammetry of oxidation of methanol on Pt@Sn(lower graph) and PtSn@Sn (upper graph) catalyst in 0.5 HCOOCH₃ and 1.0M H₂SO₄;

FIGS. 8A-D present SEM images of Pt electroless deposition on Snelectrodeposited nano-structured electrodes immersed in electrolesssolution containing 10 mM K₂PtCl₄ and 50 mM H₂SO₄ for: 5 sec (FIG. 8A),30 sec (FIG. 8B), 1 min (FIG. 8C) and 5 min (FIG. 8D); bars are 1 μm;

FIGS. 9A-C present high-resolution transmission electron microscopy(HRTEM) images of pristine Sn nano-structures (FIG. 9A) and afterimmersion in 10 mM K₂PtCl₄/50 mM H₂SO₄ solution for: 1 min (FIG. 9B), 5min (FIG. 9C);

FIG. 10 presents a graph showing the methanol oxidation on Ptelectroless deposited electrodes prepared by immersion in 10 mM K₂PtCl₄and different acid solutions (0.5 M H₂SO₄/1 M methanol solution, scanrate=20 mV/sec);

FIG. 11 presents a graph showing the UV-Vis spectra of K₂PtCl₄ in waterand K₂PtCl₄+SnCl₂ with Pt to Sn molar ratio of 1 to 5, in 80% ethyleneglycol and 20% water solutions (Pt concentration=0.1 mM);

FIG. 12 presents X-ray diffraction (XRD) patterns of Sn powder afterimmersion in 10 mM K₂PtCl₄ (a) and 10 mM K₂PtCl₄/50 mM SnCl₂ (b)solutions;

FIGS. 13A-B present sol cyclic voltammetry (CV) current vs. potentialcurves of Pt electroless deposited electrodes prepared by immersion in10 mM K₂PtCl₄ solution in 0.5 M H₂SO₄ (FIG. 13A), and 0.5 M H₂SO₄containing 1 M methanol solution (scan rate=100 mV/sec) (FIG. 13B);

FIGS. 14A-B present cyclic voltamograms of PtSn produced by electrolessdeposition on Sn electrodes prepared by immersion in 10 mM K₂PtCl₄/50 mMSnCl₂ solution in 0.5 M H₂SO₄ solution (FIG. 14A) and 0.5 M H₂SO₄/1 Mmethanol solution (scan rate=100 mV/sec) (FIG. 14B).

FIGS. 15A-B present a single cell operation of formic acid (FA) (FIG.15A) and methyl formate (FIG. 15B) on PtSn@Sn catalyst at 70° C.; arrowsmark the relevant axis of each curve;

FIGS. 16A-B present single cell operation of FA (FIG. 16A) and MF (FIG.16B) on PtSn@Sn catalyst at 70° C.; arrows mark the relevant axis ofeach curve;

FIGS. 17A-B present online Fourier transform infrared spectroscopy(FTIR) of formic acid (FIG. 17A) and methyl formate (MF; FIG. 17B)oxidation on PtSn@Sn;

FIGS. 18A-B present power vs current curves of fuel cell withelectroless deposited Pt electrode (anode: 1M methanol, cathode:humidified air);

FIG. 19 presents MF oxidation on electrodes comprised of selectedelectroless deposited catalysts (0.5 M H₂SO₄/1 M MF solution, scanrate=100 mV/sec);

FIG. 20 presents XRD patterns of PtPd and PtPdSn synthesized on Snparticles;

FIGS. 21A-D present methanol (FIG. 21A), FA (FIG. 21B), MF (FIG. 21C)and dimethyl ether (DME; FIG. 21D) oxidation on PtPd electrolessdeposited electrodes synthesized by immersion in K₂PtCl₄/PdCl₂ solutionswith different Pt:Pd atomic ratio of 1:1, 2:3 and 3:2 (0.5 M H₂SO₄/1 Mmethanol, MF, FA or DME solution, scan rate=100 mV/sec);

FIGS. 22A-D present methanol (FIG. 22A), FA (FIG. 22B), MF (FIG. 22C)and DME (FIG. 22D) oxidation on PtPdSn electroless deposited electrodessynthesized by immersion in 10 mM K₂PtCl₄/10 mM PdCl₂/50 mM SnCl₂solutions at different immersion time spans (0.5 M H₂SO₄/1 M methanol,MF, FA or DME solution, scan rate=100 mV/sec); and

FIG. 23 presents graphs showing cyclic voltammetry of Pt on lead (Pb)support in 0.5 M H₂SO₄ and 1M methanol.

DETAILED DESCRIPTION OF THE INVENTION

The present invention, in some embodiments thereof, relates toplatinum-tin based catalysts.

The present inventors have successfully designed, inter alia, a catalyststructure (e.g., in the form of a particle) comprising tin or lead film,a particle or a core, covered with the outermost layer comprising anactive metal, e.g., platinum (Pt), palladium, or any alloy thereof(e.g., Pt alloy) (hereinafter the outermost layer may be referred to as“Pt shell”). “X@Y”, or “X/Y” may denote a core shell structure, wherein“Y” represents the core and “X” represents the shell.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not necessarily limited in itsapplication to the details of construction and the arrangement of thecomponents and/or methods set forth in the following description and/orillustrated in the drawings and/or the Examples. The invention iscapable of other embodiments or of being practiced or carried out invarious ways.

According to an aspect of some embodiments of the present invention,there is provided a composition comprising an element selected from tin(Sn), lead (Pb), antimony (Sb) or a combination thereof, wherein the Pb,the Sn, the Sb, or their combination are coated by a shell, wherein theshell comprises an active metal. In some embodiments, the shell isnanosized.

In some embodiments, the Sn or the Pb are in the form of one or moreparticles.

In some embodiments, the Sn is in the form of a film. In someembodiments, the film is deposited on a support.

Herein, by “Sn”, “Sb” or “Pb”, it is further meant to encompass an alloyof each one thereof. As used herein, “Sn”, “Sb” or “Pb” assign elementsin an elemental state, wherein the term “elemental state” refers to zerooxidation state of an atom.

In some embodiments, the term “film”, as used herein, is a body having athickness which is e.g., 2, 4, 6, 8, 10, and 20 times, including anyvalue therebetween, or smaller than any of its length or widthdimensions, and typically, but not exclusively, having an overall shapeof a thin sheet.

In some embodiments, the term “film” refers to a flat or tubularstructure e.g., a sheet having substantially greater area thanthickness.

In some embodiments, the shell is characterized by a thickness of lessthan 50 nm.

Hereinthroughout, the terms “nanosized”, and “nanoparticle” (NP),describe a film, or a particle, respectively, featuring a size of atleast one dimension thereof (e.g., diameter) that ranges from about 1nanometer to 1000 nanometers.

In some embodiments, the size of the particle or of the film describedherein represents an average size of a plurality of shells ornanoparticles, respectively.

In some embodiments, the average or the median size (e.g., diameter, orlength of the particle) ranges from about 1 nanometer to 500 nanometers.In some embodiments, the average size or median ranges from about 1nanometer to about 300 nanometers. In some embodiments, the average ormedian size ranges from about 1 nanometer to about 200 nanometers. Insome embodiments, the average or median size ranges from about 1nanometer to about 100 nanometers. In some embodiments, the average ormedian size ranges from about 1 nanometer to 50 nanometers, and in someembodiments, it is lower than 35 nm. In some embodiments, the averagesize or median is about 1 nm, about 2 nm, about 3 nm, about 4 nm, about5 nm, about 6 nm, about 7 nm, about 8 nm, about 9 nm, about 10 nm, about11 nm, about 12 nm, about 13 nm, about 14 nm, about 15 nm, about 16 nm,about 17 nm, about 18 nm, about 19 nm, about 20 nm, about 21 nm, about22 nm, about 23 nm, about 24 nm, about 25 nm, about 26 nm, about 27 nm,about 28 nm, about 29 nm, about 30 nm, about 31 nm, about 32 nm, about33 nm, about 34 nm, about 35 nm, about 36 nm, about 37 nm, about 38 nm,about 40 nm, about 42 nm, about 44 nm, about 46 nm, about 48 nm, or 50nm, including any value and range therebetween.

In some embodiments, the term “shell”, as used herein, refers to thecoating domain surrounding the film.

In some embodiments, by “film is coated by a shell” it is meant to referto a composition of two or more entities, namely an entity that definesan enclosure (the enclosing entity, e.g., the shell) and the entity (orentities) that is being at least partially enclosed therein, i.e. thefilm. In addition, in some embodiments, the coating may be conformalwith the exact contour of the film.

A film or particle(s) coated by a shell may be characterized by discreteinner and outer surfaces wherein the inner surface constitutes theboundary of the enclosed area or space. The enclosed area or space maybe secluded from the exterior area of space which is bounded only by theouter surface.

In some embodiments, the closure of the enclosing entity depends on thesize, shape and chemical composition of the entity that is beingenclosed therein, such that the enclosing entity may be “closed” for oneentity and at the same time be “open” for another entity. For example,structures presented herein may be closed with respect to certainchemical entities which cannot pass through their enclosing shell, whilethe same “closed” structures are not closed with respect to otherentities.

In some embodiments, the tin film is in a dendritic form (also referredto “structure”, or “shape”, interchangeably). In some embodiments, thetin film is at least partially oxidized (e.g., in the form of SnO₂ orSnO).

In some embodiments, the term “core-shell” refers to a mixed phasecomprising metal or metal oxide, or any combination thereof.

In some embodiments, the term “dendritic structure” herein employedrefers to a structure having flake-shaped (flaky) substructures. In someembodiments, these structures are constituted by aggregation ofparticles are gathered in a large number while having branch points.

In some embodiments, the length in lateral direction of one of the flakysubstructures is from 5 nm to 200 nm. Incidentally, the term “length inlateral direction” herein employed refers to a smallest dimension withina plane of one flake.

In general, dendritic compounds comprise a core and/or a focal point anda number of generations of ramifications (also known and referred to as“branches” or “branching units”) and an external surface. Thegenerations of ramifications are composed of repeating structural units,which extend outwards radially from the core or of the focal point. Insome embodiments, dendrimers are also referred to as structurescharacterized by a tree-like structure and are built from severaldendron units that are all connected to a core unit via their focalpoint. Typically, but not exclusively, dendritic macromolecules possessa perfectly cascade-branched, highly defined, synthetic structure,characterized by a combination of high-group functionalities and acompact structure.

In some embodiments, Sn film is in the form of dendritic structurehaving a stem and branches characterized by a ratio of 1:1 to 10:1,respectively. In some embodiments, Sn film is in the form of dendriticstructure having a stem and branches characterized by a ratio of 1:1 to5:1, respectively.

In some embodiments, the term “alloy” refers to a monophasic orpolyphasic metallic material of a binary or polynary system. In someembodiments, the starting components (e.g., alloy elements) may enterinto metallurgical interactions with one another and thereby lead to theformation of new phases (e.g., mixed crystals, intermetallic compounds,super-lattice).

In some embodiments, the alloy can include deposition of two or moretarget materials, so as to form a di-segmented nanostructure (e.g., iftwo or more target metals are deposited sequentially), a tri-segmentednanostructure (e.g., if three or more target metals are depositedsequentially), etc. In some embodiments, at least one of the depositedmetals may be etched at later stages of the process. The disclosedprocess may include the deposition of one or more such target materials.

Representative example of target materials suitable for the presentembodiments, include, without limitation, metals, semiconductormaterials and organic polymers.

Non-limiting exemplary metals that are suitable for use in the contextof any of the embodiments described herein include any metal or a metalalloy that is compatible with electrochemical deposition. In someembodiments, the selected metal has properties (e.g., electricalproperties) that can be utilized in nanoscale applications. Metalalloys, comprising two or metals as described herein, are alsocontemplated, as exemplified in the Examples section below.

In some embodiments, the metal is an active metal (M).

The term “active metal” used herein means a metal such as, without beinglimited thereto, transition metals which presents catalytic activity.

Non-limiting examples M are platinum (Pt), palladium (Pd), rhodium (Rh),iridium (Ir), Sn, lead, antimony, ruthenium (Ru), iridium, molybdenum,cobalt, iron, manganese, osmium, or a combination or alloy thereof.

Deposition of metal alloys may be performed either by co-depositing(simultaneously) the metals from two or more separate electrolytesolutions, each containing ions of a different metal, or by depositingan electrolyte solution that contains a mixture of metal ions.Representative examples include, without limitation, gold (Au), silver(Ag), platinum (Pt), nickel (Ni), titanium (Ti), titanium tungstide andindium-tin-oxide.

In some embodiments, the shell comprises Pt. In some embodiments, theshell comprises Pd. In some embodiments, the shell comprises Pt and Pd.

In some embodiments, the shell comprises Pt and Pd in a ratio of e.g.,5:1, 4:1 2:1, 1.5:1, 1.4:1, 1.3:1, 1.2:1, 1.1:1, 1:1, 1:1.1, 1:1.2,1:1.3, 1:1.4, 1:1.5, 1:2, 1:3, 1:4, or 1:5, respectively, including anyvalue, ratio and range therebetween (herein throughout, by “ratio” it ismeant to refer to molar ratio).

In some embodiments, the shell comprises Pt and Pd in a ratio of from1.5:1 to 1:1.5, respectively.

In some embodiments, the desired Pt to Pd ratio may be predetermined soas to fit the material to be oxidized. For example, methyl formate (MF)may oxidize at a higher ratio of Pt to Pd, respectively. Furtherembodiments of the catalyst are described in the Examples section below.

In some embodiments, the core or the mixed phase comprise Sn, Pb,antimony, or an oxide thereof, and the shell or the other phase withinthe mixed phase comprise Pt, Pd, or their combination. In someembodiments, the ratio of Pt or the Pd (e.g., within the shell) to Sn(e.g., within the core) is from 10:1 to 1:10, or, in some embodiments,from 1:5 to 5:1, or in some embodiments, from 3:1 to 1:3, e.g., 3:1,2:1, 1:1, 1:2, or 1:3, including any value and range therebetween. Insome embodiments, the ratio is from 1:4 to 1:5. In some embodiments, thewhen deposited on tin dendrites the Pt (or the Pd) to Sn ratio may behigher according to the agent to be oxidized. Further embodiments aredescribed in the Examples section that follows.

In some embodiments, the composition is in the form of a mixed phasecomprising an oxide of Sn, and Pt and Pd, wherein the ratio of Pt to Snis from 3:1 to 1:3, e.g., 3:1, 2:1, 1:1, 1:2, or 1:3, including anyvalue and range therebetween.

In some embodiments, the Sn nano-structure allows to enhance theelectro-oxidation process due to the synergistic effect of Sn on thenoble active metal.

In some embodiments, the shell comprises an active metal and an elementselected from Sn, lead (Pb), Ru, selenium (Se), or any combinationthereof.

In some embodiments, the composition further comprises a substrate.Without being bound by any particular theory or mechanism, it is assumedthat the durability of the catalyst may be improved because of the“anchoring” effect of the Sn to a substrate.

In some embodiments, the composition comprises a core made of Pb and ashell comprising: Pt, PtSn, PtPd, PtPdSn, or PtPdSnO_(x). In someembodiments, such compositions may be placed e.g., in an acid solution,and be utilized for oxidation of fuel as described herein e.g.,methanol).

In some embodiments, the Sn (e.g., Sn film) is deposited on at least onesurface of the substrate.

In some embodiments, the composition further comprises a substrate,wherein the Sn film is:

(a) deposited on at least one surface of the substrate;

(b) coated by the material comprising the one or more metal (e.g.,active metal NPs).

Herein, in some embodiments, a plurality of the NPs is characterized bya size of from about 1 to about 100 nanometers, or from about 1 to about50 nanometers, or in some embodiments, from about 1 to about 10nanometers.

Herein, the term “size” may refer to either the average of at leaste.g., 70%, 80%, or 90% of the particles, or in some embodiments, to themedian size of the plurality of nanoparticles.

For simplicity, the expression “deposited on at least one surface” isalso referred to herein, as a coating on a substrate, or as a substrateor surface having a film deposited thereon, or on a portion thereof. Insome embodiments, the Sn film is incorporated in and/or on at least aportion of the substrate. In some embodiments, the term “coating” andany grammatical derivative thereof, is defined as a coating that (i) ispositioned above the substrate, (ii) is not necessarily in contact withthe substrate, that is to say one or more intermediate coatings may bearranged between the substrate and the coating in question, or (iii)does not necessarily completely cover the substrate.

Substrate usable according to some embodiments of the present inventionmay comprise, for example, organic or inorganic surfaces.

In some embodiments, the substrate is selected from, but is not limitedto, carbon, a metal oxide, a polymer, or any combination thereof.

Non-limiting exemplary substrates are selected from activated carbon,graphite, carbon nanotube, metal mesh or foam, ceramic materials, or anycombination thereof.

Fuel Cell

In some embodiments, there is provided a fuel cell having anelectrocatalyst comprising the disclosed composition. In someembodiments, the electrocatalyst is the anode.

In some embodiments, the term “electrocatalyst” refers a specific formof catalyst that functions at electrode surfaces or, in someembodiments, may be the electrode surface itself.

In some embodiments, the term “fuel cell” is a device that converts thechemical energy from a fuel into electricity through a chemical reactionof positively charged hydrogen ions with oxygen or another oxidizingagent.

The present inventors have now surprisingly uncovered that the disclosedelectrocatalyst shows enhance activity toward the oxidation of fuels.

In some embodiments, the fuel cell is used for the oxidation of fuels,such as, and without being limited thereto, methanol, ethanol, formicacid (FA), formaldehyde, and glucose.

In some embodiments, the fuel(s) are delivered to the disclosed fuelcell in high vapor pressure (low boiling point), enabling their supplyas fumes/gas directly to the cell anode.

In some embodiments, the electrode preparation methods described herein,are utilized in manufacturing various types of fuel cells, including,without limitation, phosphoric acid electrolyte fuel cells, polymerelectrolyte fuel cells, and alkaline fuel cells.

In some embodiments, the electrocatalyst is characterized by an improvedelectrochemical surface area. In some embodiments, the electrocatalystis characterized by an electrochemically active surface area of e.g., atleast 30 m²g⁻¹ at least 40 m²g⁻¹, at least 50 m²g⁻¹, at least 60 m²g⁻¹,at least 75 m²g⁻¹, or at least 80 m²g⁻¹.

Exemplary fuel cells are described in the Examples section that follows.The practiced fuel cells show high electrical efficiency for longperiods of continuous operation.

In some embodiments, the current-density peak for FA oxidation on thedisclosed catalyst is between 100 mA/mg to 500 mA/mg. In someembodiments, the current-density peak for FA is between 250 mA/mg to 300mA/mg. In some embodiments, the current-density peak for MF oxidation onthe disclosed catalyst is between is between 100 mA/mg to 500 mA/mg. Insome embodiments, the current-density peak for FA is between 220 mA/mgto 270 mA/mg.

In some embodiments, the peak of power density delivered by fuel cellusing the disclosed catalyst for FA is between 0.050 mW/mg to 0.100mW/mg. In some embodiments, the peak of power density delivered by fuelcell using the disclosed catalyst for FA is between 0.070 mW/mg to 0.090mW/mg. In some embodiments, the peak of power density delivered by fuelcell using the disclosed catalyst for MF is between 0.050 mW/mg to 0.100mW/mg. In some embodiments, the peak of power density delivered by fuelcell using the disclosed catalyst for FA is between 0.050 mW/mg to 0.070mW/mg.

As exemplified in the Examples section below, the current-density peakfor FA and MF oxidation on PtSn@Sn catalyst is 275 mA/mg and 240 mA/mg,respectively. Similarly, the peak of current-density for FA and MFoxidation on Pt@Sn catalyst is 200 mA/mg and 190 mA/mg, respectively.The peak of power density delivered by laboratory prototype fuel cellusing PtSn@Sn catalyst for FA and MF is 0.085 mW/mg and 0.060 mW/mg,respectively.

As further exemplified in the Examples section below, the practiced fuelcells efficiently perform with various air cathodes (having differentcatalysts) and with various solid membrane separators. A fuel cellsystem containing a uniquely designed solid membrane separator may alsobe practiced.

In some embodiments, the fuel cell system described herein operates atroom temperature, although higher temperatures are also contemplated,e.g., 30° C., 40° C., 35° C., 60° C., or 70° C.

The catalyst described herein may be introduced into a reformed fuelcell system. For example, biofuels may be used in these reformed fuelcell system as the primary fuel, wherein a means of recovering hydrogengas is required. In some embodiments, the disclosed catalyst may be usedin carbon monoxide contaminated fuel.

Preparation Methods

In some embodiments, there is provided a process for manufacturing thedisclosed electrocatalyst, e.g., electrocatalyst comprising a substrateas described above, having attached thereon an Sn film, wherein: the Snfilm is coated by one or more active metal NPs and optionally by anelement selected from, without being limited thereto, Sn, ruthenium(Ru), selenium (Se), or any combination thereof.

In some embodiments, the process comprises the steps of: (i)electrodepositing the Sn film on the substrate; and (ii) plating amaterial comprising the active metal NPs and optionally the M on the Snfilm, thereby obtaining the catalyst.

In some embodiments, step (ii) is performed by electroplating. In someembodiments, step (ii) is performed by electroless plating of a metalsubstance on a substrate, e.g., conducting substrate, as describedherein throughout. In some embodiments, step (ii) is performed byelectrodeposition.

In some embodiments, electroless deposition (plating) refers to acatalytic or autocatalytic process whereby a chemical reducing agentreduces a metallic salt onto specific sites of a catalytic surface whichcan either be an active substrate or an inert substrate seeded with anactive metal.

In some embodiments, electroless deposition (plating) refers to achemical process of oxidation and/or reduction by which a metallic ionis reduced from a solution (e.g., an aqueous solution) containing areducing agent on a surface having a lower standard reduction potentialcatalytic site without the need of applying a current. As furtherdescribed in the Examples section below, a viscous liquid or a solutionthereof (e.g., aqueous solution), for example, and without limitation,ethylene glycol or propylene glycol, may be utilized, thereby assistingobtaining a uniform coating.

In accordance with some embodiments of the present disclosure,electroless deposition provides a method for controlled deposition ofPt, Pb, or other metal atoms on Sn previously deposited on a carbonsupport. In some embodiments, during electroless deposition, thetemperature, and concentrations of metal salts, reducing agents, and ofcomplexing agents may be modified to give controlled rates of metaldeposition on the seed nuclei. Thus, it becomes possible to chemicallydeposit Pt onto Sn, resulting in the formation of very small metalparticles having surface/volume ratios approaching unity. In someembodiments, in this manner, the required loading of Pt necessary forsatisfactory fuel cell performance can be dramatically lowered,resulting in significant savings on fuel cell costs.

In some embodiments, the use of electroless deposition to fabricatePt-containing electrocatalysts results in the formation of smallparticles that possess core-shell geometry. This geometry offers thepossibility of improving many aspects of fuel cell performance. Inaccordance with certain aspects of the present disclosure, the core canbe some metal other than Sn. Without being bound by any particulartheory, it is assumed that if the e.g., Pt shell thickness is thinenough, the core metal may be close enough to the surface to perturb thephysical properties of the Pt surface layer (shorter Pt—Pt latticeparameters) and electronic properties of the surface Pt sites (Ptd-orbital vacancies).

In some embodiments, step (ii) is performed by a technique which isuseful for depositing metallic coatings onto substrates, for example,and without being limited thereto, sputtering, chemical vapordeposition, ion beam enhanced deposition, plasma-assisted vapordeposition, cathodic arc deposition, or ion implantation andevaporation.

In some embodiments, step (ii) is performed by chemical reduction. Thereare several different reducing agents that may be used for electrolessdeposition in accordance with some embodiments of the present disclosurethat include, but are not limited to, sodium hypophosphite, ethyleneglycol, hydrazine, dimethyl-amine borane, diethyl-amine borane, sodiumborohydride, formaldehyde, and hydrogen gas.

In some embodiments, the electrochemical deposition is accomplished bythe reduction of metal ions from an electrolytic solution through theapplication of a negative potential. This may be performed for instance,at cyclic voltammetry mode, galvanic displacement, galvanostatic mode(constant current), or potentiostatic (constant voltage) mode orcyclic-voltammetry conditions.

As a specific embodiment, the method for preparing a PtSn nanoparticlecatalyst includes preparing a precursor solution of Pt salt, and inanother specific embodiment, the solution for galvanic deposition ofPtSn alloy on Sn is prepared by dissolving K₂PtCl₄ and SnCl₂ in ethyleneglycol and water (e.g., 80:20) containing H₂SO₄.

Further embodiments of this section are presented in the Examplessection below.

General

As used herein the term “about” refers to ±10%.

The terms “comprises”, “comprising”, “includes”, “including”, “having”and their conjugates mean “including but not limited to”. The term“consisting of means “including and limited to”. The term “consistingessentially of” means that the composition, method or structure mayinclude additional ingredients, steps and/or parts, but only if theadditional ingredients, steps and/or parts do not materially alter thebasic and novel characteristics of the claimed composition, method orstructure.

The word “exemplary” is used herein to mean “serving as an example,instance or illustration”. Any embodiment described as “exemplary” isnot necessarily to be construed as preferred or advantageous over otherembodiments and/or to exclude the incorporation of features from otherembodiments.

The word “optionally” is used herein to mean “is provided in someembodiments and not provided in other embodiments”. Any particularembodiment of the invention may include a plurality of “optional”features unless such features conflict.

As used herein, the singular form “a”, “an” and “the” include pluralreferences unless the context clearly dictates otherwise. For example,the term “a compound” or “at least one compound” may include a pluralityof compounds, including mixtures thereof.

Throughout this application, various embodiments of this invention maybe presented in a range format. It should be understood that thedescription in range format is merely for convenience and brevity andshould not be construed as an inflexible limitation on the scope of theinvention. Accordingly, the description of a range should be consideredto have specifically disclosed all the possible subranges as well asindividual numerical values within that range. For example, descriptionof a range such as from 1 to 6 should be considered to have specificallydisclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numberswithin that range, for example, 1, 2, 3, 4, 5, and 6. This appliesregardless of the breadth of the range.

Whenever a numerical range is indicated herein, it is meant to includeany cited numeral (fractional or integral) within the indicated range.The phrases “ranging/ranges between” a first indicate number and asecond indicate number and “ranging/ranges from” a first indicate number“to” a second indicate number are used herein interchangeably and aremeant to include the first and second indicated numbers and all thefractional and integral numerals therebetween.

As used herein the term “method” refers to manners, means, techniquesand procedures for accomplishing a given task including, but not limitedto, those manners, means, techniques and procedures either known to, orreadily developed from known manners, means, techniques and proceduresby practitioners of the chemical, and electronical arts.

In those instances where a convention analogous to “at least one of A,B, and C, etc.” is used, in general such a construction is intended inthe sense one having skill in the art would understand the convention(e.g., “a system having at least one of A, B, and C” would include butnot be limited to systems that have A alone, B alone, C alone, A and Btogether, A and C together, B and C together, and/or A, B, and Ctogether, etc.).

It will be further understood by those within the art that virtually anydisjunctive word and/or phrase presenting two or more alternative terms,whether in the description, claims, or drawings, should be understood tocontemplate the possibilities of including one of the terms, either ofthe terms, or both terms.

For example, the phrase “A or B” will be understood to include thepossibilities of “A” or “B” or “A and B.”

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

EXAMPLES

Reference is now made to the following examples, which together with theabove descriptions illustrate some embodiments of the invention in anon-limiting fashion.

Materials and Methods

Tin chloride and methyl formate were purchased from SIGMA ALDRICH™.

Potassium tetrachloroplatinate (K₂PtCl₄) were purchased from STREM™Chemicals. Methanol, formic acid, sulfuric acid, nitric acid andethylene glycol were purchased from MERCK®. TORAY™ carbon sheet (TGPH090™) was purchased from fuel cell stores. Commercial PlatinumRuthenium (50:50) and platinum black catalyst was purchased from ALFAAESAR™ and BASF™ respectively. All reagents were of analytical grade andwere used without any further purification. NAFION® 115 membrane waspurchased from ION POWER™, INC. Deionized water with resistivityof >18.0 MΩ was used throughout the synthetic processes andelectrochemical measurements.

Preparation of Catalysts:

Electro-deposition of tin was performed on one square centimeter ofTORAY™ carbon. The solution for electro-deposition was prepared bydissolving tri sodium citrate (0.05M) and tin chloride (0.018M) indeionized water. Tin chloride solution (25 ml) was purged with nitrogenand electro-deposition was performed using chronoamperometry. Thepotential and charge used for electro-deposition was −3.0V and 10 C,respectively. After tin deposition electrodes were washed with deionizedwater then with acetone and dried under nitrogen.

Four types of solutions were prepared for electroless process andfabricated electrodes were named accordingly, as presented in Table 1:

TABLE 1 Sample No. Solution Catalyst Code Solution 1. Platinum Platinumon Tin Pt on Sn Water + H₂SO₄ 2. Platinum Platinum Tin on PtSn onWater + EG Tin Tin Sn (ethylene glycol) + H₂SO₄

The solution for electroless deposition of platinum (K₂PtCl₄) wasprepared by dissolving corresponding salts (10 mM) in deionized watercontaining 50 mM of H₂SO₄. The solution for galvanic deposition of PtSnalloy on Sn was prepared by dissolving K₂PtCl₄ (10 mM) and SnCl₂ (50 mM)in ethylene glycol and water (80:20) containing 50 mM of H₂SO₄. Thesolution was purged with nitrogen before electroless deposition andelectrodes were washed with deionized water, then with acetone and weredried under nitrogen. After electrochemical testing all of theelectrodes were dissolved in aqua-regia and diluted to 100 times indeionized water for ICP analysis.

Preparation of Electrodes for Fuel Cell

The anode for fuel cell was fabricated by electro-deposition andgalvanic replacement, as described herein, on TORAY® carbon. The cathodewas fabricated by pasting commercial platinum black on carbon cloth.Platinum black was mixed with carbon powder, NAFION® and TEFLON®solution and deposited on carbon cloth. The loading of catalyst on anodeand cathode side was 0.3 mg/cm² and 5.0 mg/cm². Nafion® 117 wasactivated by boiling in sulfuric and nitric acid and stored in deionizedwater. A membrane electrode assembly was made using a laboratoryprototype fuel cell. Humidified air was supplied at cathode side therate of 200 ml/min and 1.0 M fuel (Methyl Formate and Formic Acid)dissolved in water was circulated using peristaltic pump at the flowrate of 25-30 ml/min. The performance of cell was examined at differenttemperature. The cell was tested under load using CHROMA™ 63102 DC™electric load.

Physical and Electrochemical Characterization

The microstructure of electrodes was analyzed by scanning electronmicroscopy (Hitachi S-4800 SEM). The amount of active metals (Pt/Pd)deposited on electrodes were analyzed by Varian ES-715 inductive coupledplasma (ICP). The electrochemical testing was performed at roomtemperature on CHI 760C and Bio-logic VSP electrochemical workstationsusing a conventional three-electrode cell with Pt mesh as counterelectrode and Ag/AgCl (3.0 M KCl) reference electrode. The activation ofthe catalyst was performed by cycling in sulfuric acid in the potentialrange of −0.22V to 1.0V at scan rate of 100 mV/s. The oxidation of fuelswas studied in 0.5M H₂SO₄ as supporting electrolyte containing 1.0 M offuel (Formic acid and Methyl Formate). The X-ray diffraction (XRD)patterns were recorded on X-ray diffractometer (PAN analytic) using CuKα radiation (λ=1.54 Å). The gaseous by products were collected in a gaschamber and online FTIR was performed using Bruker spectrophotometer.Fuel cell tests were performed using laboratory prototype fuel cell(Electrochem). The cell performance was tested at differenttemperatures, using Chroma 63102 DC electric load. The online FTIRanalysis of gaseous products of FA and MF oxidation was performed on alaboratory prototype fuel cell operating at constant temperature. Thegaseous products were collected at different potentials (0.2V, 0.4V,0.6V, 0.8V, and 1.0V). The FTIR gas cell was purged with nitrogen totake background and gaseous products were collected in evacuated gascell. The instrument was purged with high-purity nitrogen gas andinterferograms were collected at 4 cm′ resolution.

The fuel cell anode acts as working electrode and the cathode works bothas counter and reference electrode. As noted above, formic acid andmethyl formate (1.0M) in deionized water was circulated at the rate of25-30 ml/min and humidified hydrogen on cathode side at the flow rate of10 ml/min.

Example 1 Platinum-Tin Catalysts Via Galvanic Displacement

Material Characterizations

The scanning electron microscopy image of electro-deposited tindendrites on porous carbon current collector (TORAY®) is shown in FIGS.1A-B. The tin was electro-deposited at different potentials and it wasfound that the length and distribution of tin dendrites was more uniformwhen deposited at higher over potential (−3.0 V). The average length ofdendrite's stem was 125-150 μm and side branches were 5-8 μm. The tindendrites preserved their structure even after galvanic displacement byPt of Pt@Sn and PtSn@Sn catalyst. The typical diameter of PtSn@Sn andPt@Sn nanoparticles observed at higher magnification was 5-8 nm and30-45 nm, respectively (as shown in FIGS. 2A-B and 3A-B, respectively).The energy dispersive X-ray mapping of tin dendrites revealed uniformdistribution of platinum nanoparticles across the surface of thesupporting Sn.

Electrochemical Testing

The electrochemical activity of all catalysts for oxidation of formicacid and methyl formate was investigated by cyclic voltammetry (CV)measurements in standard 3 electrode cell. The CV of electrodes insupporting electrolyte (0.5M H₂SO₄) is presented in FIG. 4.

The H-adsorption/desorption peaks are exhibited by all catalysts inpotential range −0.2-0.1 V and peaks for formation/reduction of Pt oxidecould be observed at 0.5-0.6 V. The hydrogen adsorption/desorption peaksof PtSn@Sn catalyst is slightly higher than Pt@Sn, that results fromhigher active electrochemical surface area of PtSn catalysts. Thespecific electrochemical active surface areas of platinum basedcatalysts were calculated from desorption charge of hydrogen atoms.Electrochemical surface area (ECSA) was calculated for both catalystsusing following equation:

${ECSA} = \frac{Q_{H}}{\lbrack{Pt}\rbrack*0.21}$

where [Pt] represents the platinum loading (mg/cm²) on the electrode,Q_(H) denotes the charge for hydrogen desorption (mC/cm²) and 0.21represent the charge required to oxidize a monolayer of H₂ on bright Ptor monolayer of PtH_(ads). The calculated ECSA for Pt@Sn and PtSn@Sncatalyst was 23.3 m²g⁻¹ and 32.6 m²g⁻¹, respectively.

The CV of formic acid oxidation on platinum based catalyst are shown inFIG. 5. Both catalysts showed similar onset potential (−0.15V) and peakcurrent at same potential (0.76 V). Only forward sweeps of CV data areexhibited to show more clearly the electro-oxidation behavior of FA onboth catalysts. The peak current was normalized with the amount ofactive metal. PtSn@Sn showed the highest current both in low and highpotential region. Formic acid undergoes oxidation through indirectpathway on Pt based catalyst and peak current observed between 0.7 to0.8 V. In case of PtSn@Sn a strong peak is observed at the low potentialregion resulting from the oxidation of FA through direct pathway thatresults from synergistic effect between Pt and Sn alloy. Without beingbound by any particular theory, it is assumed that both pathways arestructure sensitive and the reaction rate is strongly dependent onsurface of electrode. On Pt (111) formic acid oxidizes through directpathway, but the rate of reaction is very low; hence a smallelectro-oxidation current is observed. The rate of electro-oxidation ishigh on Pt (100) surface, but formic acid oxidizes through indirectpathway. High current density in high potential region also confirmsbetter CO tolerance of PtSn@Sn as compared to Pt@Sn catalyst. The peakcurrent density (at 0.76 V) for FA oxidation on Pt@Sn and PtSn@Sn was200 mA/mg and 270 mA/mg, respectively. The total charge for formic acidoxidation, calculated by integrating the area under the curve in forwardsweep for Pt@Sn and PtSn@Sn was 2.62*10⁻³ C and 2.43*10⁻² C,respectively.

The cyclic voltammetry of electro-catalytic oxidation of methyl formateis presented in FIG. 6. The electro-oxidation of formic acid is dominantin low potential region, whereas electro-oxidation of methanol is themain reaction in high potential region. Without being bound by anyparticular theory, it is assumed that the complete electro-oxidation ofmethyl formate takes place according to the following reactions:

CH₃OCOH+H₂O→HCOOH+CH₃OH  (1)

HCOOH→CO₂+2H⁺+2e ⁻  (2)

CH₃OH+H₂O→CO₂+6H⁺+6e  (3)

The onset potential for oxidation of methyl formate on Pt@Sn and PtSn@Snis at −0.15 V and oxidation behavior was also similar in both low andhigh potential region. The current in case of PtSn@Sn catalyst wasslightly higher than that of Pt@Sn. Formic acid is preferentiallyadsorbed and oxidized at low potentials and most of the currentoriginates from its electro-oxidation. But, without being bound by anyparticular mechanism, in high potential region CO from methanol cansignificantly contribute to the majority of the observed current.

The difference in current density in low potential region for MFoxidation was not as prominent as for FA oxidation. But current densityin both low and high potential region was slightly higher in case ofPtSn@Sn catalyst. High current density measured with PtSn@Sn catalystconfirmed high activity and tolerance from CO poisoning. The peakcurrent density (0.76 V) for MF oxidation on PtSn@Sn and Pt@Sn catalystwas 240 mA/mg and 190 mA/mg respectively. The total charge for formicacid oxidation, calculated by integrating the area under the curve inforward sweep for Pt@Sn and PtSn@Sn was 2.461*10⁻³ C and 1.997*10⁻² C.

The cyclic voltagram of methanol oxidation on both catalysts is shown inFIG. 7. Platinum based catalysts oxidizes methanol and the onsetpotential for methanol oxidation on Pt@Sn and PtSn@Sn catalysts was at−0.15 V. In case of methanol electro-oxidation only one peak wasobserved at 0.78V. The maximum current at this potential was higher incase of PtSn catalyst. In all potential regions, the electro-oxidationcurrent was also higher in case of PtSn catalyst. That might be becauseof high catalytic activity and easier oxidation of CO that is generatedas intermediate during the process of the methanol oxidation on the tinsupported catalysts. In addition to superior catalytic activity, bothcatalysts showed stability during the period of measurement. The peakcurrent density for methanol oxidation on PtSn@Sn catalyst was slightlyhigher than FA acid and MF oxidation, but the total oxidation chargeshowed the trend FA>MF>MeOH. The total charge for methanol oxidation inforward sweep for Pt@Sn and PtSn@Sn was 2.996*10⁻³ C and 2.09*10⁻² C,respectively.

Example 2 PT Electroless Deposition Process

Without being bound by any particular theory, it is assumed that duringthe Pt electroless deposition process, Pt²⁺ ions from the solution aredirectly reduced by the less noble Sn metal due to the difference in thestandard reduction potentials of Sn and Pt, −0.14 and 1.2 V,respectively.

The reduced Pt atoms precipitate on the electrode whereas Sn²⁺ ionsdissolve into the solution. This spontaneous process which occursspontaneously without the need of adding another reducing agent.

FIGS. 8A-D present SEM micrographs of tin nano-particleselectrodeposited on toray paper sheet, after immersion in the Ptelectroless solution for different time spans. Acid as an additive isused to remove the oxide layer and to activate the Sn surface in orderto allow reduction of Pt²⁺ ions directly on the metallic substrate.

This approach provides lower electron transfer resistance compare to Ptdeposed on SnO₂. During the electroless process, a thin Pt layer isformed on the tin particles as may be seen by the evolution of a darklayer which gradually covers the particles. The use of diluted acidadditive results with leaching of tin and a decrease of the particlesize until the Pt deposited particles forms a protective layer whichprevents further degradation. After immersion for 5 min, the electroderemains stable even in standard 0.5 M solution and shows high reactivitytowards methanol oxidation.

HRTEM images of the Sn electrodes were inspected during the electrolessdeposition process (FIGS. 9A-C). The original structure morphology ofoxide layer seen in FIG. 9A is altered after one minute of immersionseen as surface roughening and local pitting. Longer immersion for 5minutes (FIG. 9C) clearly displayed an extensive morphological change ofthe metallic Sn bulk together with formation of Pt grains seen as darkspots on the surface. Longer immersion spans did not change the catalystlayer structure and the Sn substrate morphology was retained.

Sn tends to form oxides such as SnO and SnO₂ when exposed to ambient airor in aqueous solution. These oxide layers may hinder the Pt electrolessdeposition process leading to formation of ununiformed Pt layers, whichdecrease the Pt utilization and the electrode performance. To avoid thiseffect, the Pt electroless deposition was performed in several acidcontaining solutions which the Sn electrodes were immersed in for 5minutes.

The Pt content of the electrodes was measured by ICP after a stableelectrochemical performance was attained. FIG. 10 shows current vs.potential curves of methanol oxidation on the attained electrodes. Itmay be seen that the best performance is attained when the solutioncontained 0.05 M H₂SO₄ despite the somewhat lower Pt content in thissample (63 μg/cm² compared with 70 μg/cm² and 85 μg/cm² for 0.025 MH₂SO₄ and 0.1 M HClO₄, respectively). This implies on the formation of auniform Pt layer in this solution which leads to better utilization ofthe catalyst. It should be noted that at higher acid concentrations, Sndissolution has a detrimental effect on the electrodes due to thesupport and active catalyst losses.

Next, electroless deposition of PtSn alloy on the Sn dendrite electrodeswas studied. The undertaken approach exploit Pt—Sn complexes formedbetween SnCl₂ and PtCl₄. FIG. 11 shows UV-Vis spectra of K₂PtCl₄/SnCl₂mixture in 80% ethylene glycol and 20% water in Pt to Sn molar ratio of1 to 5, respectively. The later solvent ratio was optimized as the bestcomposition for the electroless reduction of the Pt—Sn complexes. Anyfurther increase in the water content leads to instantaneousprecipitation of the solid products and lower Pt yield. In solution of100% ethylene glycol no substantial electroless process was observed.

It should be noted that the Pt(II) to Sn(II) molar ratio of 1 to 5 waschosen in order to allow full substantiation of all the Cl ligands bySnCl₃ during the complexation reaction to form the stable [Pt(SnCl₃)₅].The Pt UV-Vis spectrum in FIG. 11 shows a typical peak of [PtCl₄]²⁻ at248 nm, whereas a new peak appears at 300 nm and a broad wave up to 600nm in the Pt—Sn spectrum, attributed to the formation of the Pt—Sncomplexes, presumably [Pt(SnCl₃)_(x)Cl_(5-x)]²⁻ (x=1-5).

ICP analysis of the PtSn alloy atomic composition was performed byelectroless deposition on Pb electrodeposited electrodes which wereimmersed in identical 1:5 K₂PtCl₄/SnCl₂ solution. Pb was selected as thetest substrate for two reasons—first—deposited tin cannot bedistinguished from the bulk Sn substrate and secondly, the closestandard reduction potential of Pb²⁺ and Sn²⁺: −0.1205 V and −0.1375 V,respectively, close enough to simulate similar reduction conditions. Inthese ICP measurements, Pt and Sn in molar ratio were 1 to 1.8.

Voltammetric study of Pt—Sn complexes reduction at early stages ofelectroplating on a gold working electrode shows that the onsetpotential of the electroplating process shifts to higher overpotentialof −0.5 V compared with 0.4 V of Pt²⁺ and −1.1 V of Sn²⁺ reduction.These values are much more positive than the Sn and Pb reductionpotentials, enabling the electroless deposition reaction of the formedcomplexes on those substrates. This also implies on the presence of thecomplex and its reduction potential which is higher than the Sn one.

Attempts to perform XRD measurements on Pt and PtSn electrolessdeposited on Sn dendritic electrodes was unsuccessful due to the lowthickness of the noble metal layer. Hence, Sn powder with an averageparticle size of 10 μm was stirred in solution of 10 mM K₂PtCl₄ and 50mM SnCl₂ for 24 h and characterized by XRD. Most of the peaks in the Ptpattern are assigned to the Sn substrate including the main peaks at 20values of 31.01° (200), 32.89° (101), 44.16° (220) and 45.15° (211).Only Pt (111) peak at 40.16° is seen in this pattern, due to the lowloading of the Pt layer formed on the Sn particles surface area (FIG.12). There was no evidence of Pt—Sn intermetallic bonds formed duringthe electroless process found in these measurements. However, in PtSnpattern, new peaks obtained at 20 (2-theta) values of 15.78°, 21.71°,42.51°, 66.88°, and 75.66°. A multiple overlapping peak in the 2-thetarange of 33.50° to 37.50° were also observed. The exact assignment ofthe peaks to known stoichiometric compounds may include PtSn, PtSn₂ orPtSn₄.

Methanol Oxidation on Catalysts Prepared by Electroless Deposition:

The electroactivity of methanol oxidation on catalysts prepared byelectroless deposition on Sn dendrite electrodes towards methanoloxidation was studied using Pt@Sn and PtSn@Sn electrodes. FIG. 13A showsthe current vs. potential curves of Pt@Sn steady state voltammogram. Twoelectrodes that are shown were prepared by electroless process for 2.5min (E1) and 5 min (E2), respectively. Interestingly, despite thedifferent electroless process time span, the Pt loading on bothelectrodes was about 25μ.g.

As shown above (FIGS. 8A-D and 12), during the electroless process whichoccurs in an acidic solution, the Sn substrate nano-structures werepartially dissolved resulting with the loss of the active material untilmore homogeneous Pt layer is formed on the Sn nano-structures surfacearea. Electrochemical surface area calculated from the hydrogendesorption region for electrode E2 is 11.6 m²/g which is higher than1.72 m²/g of electrode E1. Methanol oxidation follow the same trendshowing higher CO oxidation peak of E2 over E1 (FIG. 13B), whereas theintegrated oxidation charges are 200.0 mC and 50.2 mC, respectively. Itseems that longer the electroless time spans, results with more uniformlayers of Pt are formed, resulting in higher utilization of the Pt.

FIGS. 14A-B show the same measurements for electrodes E3 and E4 preparedin 10 mM K₂PtCl₄ and 50 mM SnCl₂ in ethylene glycol electrolesssolution, by 15 and 30 min immersion in the electroless solution,respectively. Longer time spans were needed to obtain substantialcatalysts deposition due to the slower nature of the electrolessreaction in the ethylene glycol solution. In this case, longerelectroless reaction time span gave rise to lower ECSA values of 23.5m²/g for the electrode prepared at long immersion time span of 30 min(E4) compared to 86.4 m²/g for the electrode prepared at short immersiontime of 15 min (E3), although in both electrodes the Pt loading wasabout 50 μg/cm². This is also reflected by the integrated charge of COoxidation on both electrodes, 875 mC and 510 mC for E4 and E3,respectively. In this case, longer immersion time spans of 30 min,results with the loss of some of the Sn substrate dissolved leavinglower surface area for the PtSn deposition which forms thicker catalystlayers with low electroactivity.

A comparison of Pt and PtSn catalysts undoubtedly show the 5-foldenhanced peak oxidation current of PtSn@Sn. This is attributed toco-catalysis effect of Sn on Pt that facilitates the catalystselectroactivity due to electronic effect as well as oxophilicbi-functional contribution from the SnO_(x).

Taken together, it can be concluded that Pt@Sn and PtSn@Sn electrodeswere synthesized by one step, binder free electroless deposition method.The active material forms a thin layer on the pre-electrodeposited Snnano-structures. The acidity of the electroless solution must becarefully adjusted in order to remove some of the oxide layers coveringthe Sn substrate thus hindering the electroless process, withoutdissolving the Sn substrate to a large extent. PtSn species weredetected on the Sn substrate which was immersed in Pt and Sn precursorssolution by XRD measurements, due to the formation of Pt—Sn complexeswhich undergo reduction during the electroless process. The ECSA and theelectrodes activity towards methanol oxidation is prone to theelectroless process time span.

Shorter or longer immersion time in the electroless solution resultswith uniform active material deposition and low electroactivity. Fuelcell measurements of the attained electrodes showed the higherelectroactivity of the electrolessly deposited Pt@Sn and PtSn@Snelectrodes over commercial PtRu electrodes in terms of higher peak powerand potential, due to the unique structure of these electrodes as wellas a synergistic effect of the Sn substrate on the electroactivity ofthe active metal. These encouraging results give rise to furtherdevelopment of catalysts deposited on metallic substrates as thin layersfor the oxidation of methanol and other fuels, utilizing electrolessdeposition technique.

Example 3 Electro-Oxidation Testing

The Galvanic Method

The performance of a single cell using Pt@Sn and PtSn@Sn anode catalystsfor electro-oxidation of methyl formate and formic acid was examined andcompared with the commercial PtRu@C (E-TEK) anode. The single celltesting was performed in the temperature range of 30-70° C. Anode andcathode catalysts were activated by running the cell under hydrogenbefore changing the fuels. The flow rate of methanol was kept low tomitigate the problem of crossover. The performance of single cell hasillustrated in FIGS. 15A-B and FIGS. 16A-B. The maximum power densitydelivered by fuel cell depends on the loading of catalyst. The powerdensity both in terms of geometrical surface area and loading ofcatalyst was normalized. The maximum power density for formic acidoxidation on Pt@Sn and PtSn@Sn was 0.055 W/mg and 0.085 W/mg,respectively. The gravimetric power density of PtSn@Sn catalyst was 3times higher than the same catalyst prepared by the polyol method.PtSn@Sn exhibited the highest power output for electro-oxidation allfuels.

The Pt@Sn anode catalyst also exhibited superior performance towardformic acid and methyl formate oxidation as compared to commercial PtRucatalyst. The maximum power density for methyl formate oxidation onPtSn@Sn and Pt@Sn catalyst was 0.60 W/mg and 0.45 mW/mg respectively.Moreover, the maximum power density for methanol oxidation is alsohigher than the commercial PtRu catalyst. The performance of Pt@Sncatalyst is comparatively lower than that of the PtSn@Sn but higher thanthat of the commercial PtRu catalyst.

Online FTIR Spectroscopic Study of Fuel Oxidation:

The main gaseous product of formic acid oxidation was CO₂. Increase inoperating potential of cell CO₂ concentration gradually increases thegaseous product. The FTIR spectra of gaseous products are shown in FIGS.17A-B.

At low potential (0.2V) characteristic peak for formic acid was observedat 1730 cm⁻¹ and 1250 cm⁻¹ that is derived from C=0 and C—O stretching,respectively. Formic acid oxidizes through dehydration and oxidation ofadsorbed CO (CO_(ad)). Linearly and multiply bonded CO_(ad) andbridge-bonded formate are the only detectable intermediates. Theseintermediates are also bounded to catalyst surface so are not detectablein gaseous product. The only detectable gaseous product is carbondioxide and the characteristic peak was observed at 2350 cm⁻¹ thatgradually increases with the increase in applied potential. Withoutbeing bound by any particular mechanism it is assumed that the intensityof formic acid peaks gradually decreases because of the fast kinetics ofelectro-oxidation and relative low volatility. The electro-oxidationpathway for formic acid on Pt is also potential dependent. The maingaseous product CO₂ was detected at all potentials that revealelectro-oxidation of formic acid through direct pathway. Theelectro-oxidation of formic acid through direct pathway is furtherconfirmed by dominant peak in low potential region in the voltagram.

The peaks for MF were observed at all potentials because of the highvolatility, but the peaks for methanol or formic acid were absent inFTIR spectra that confirm it was not hydrolysed in water in absence ofacid. The NAFION® membrane was highly acidic and MF undergoes hydrolysisonly when it reaches the membrane. The characteristics peak of methylformate was observed at 1750 cm⁻¹, 1190 cm⁻¹ and 2900 cm⁻¹ that wasderived from C═O, C—O and C—H stretching, respectively.

Similar to formic acid, the only detectable gaseous product was carbondioxide and the characteristic peak was observed at 2350 cm⁻¹ thatgradually increased with increase in applied potential. High volatilityof methyl formate resulted in strong characteristic peak at allpotential as compared to characteristics CO₂ peaks. The main poisoningintermediate CO is strongly adsorbed to the catalyst, and hence couldnot be observed in the gas phase FTIR spectrum. Beside strong peaks forMF and CO₂ peaks, no other peaks which could be attributed to partialoxidation products were observed in the spectrum which suggests eitherthat the intermediates are consumed as fast they are formed or stronglyadsorbed to the catalyst surface; hence no detectable gaseous product inthe gas phase FTIR spectra.

It can be concluded that Pt@Sn and PtSn@Sn catalyst synthesized byelectro-deposition and galvanic displacement reaction showed enhancedactivity and stability toward formic acid and methyl formateelectro-oxidation. The scanning electron microscopy and energydispersive x-ray mapping showed uniform distribution of both catalystson tin dendrites. A dominant peak in low potential region confirmselectro-oxidation of formic acid through direct pathway. Fuel cellresults also showed better performance as compared to commercial PtRucatalyst. The gravimetric power density in laboratory prototype fuelcell was 4 times higher than PtSn catalyst synthesized by the polyolmethod.

The Electroless Method

The electroactivity of the prepared electrodes was evaluated as fuelcell anodes in a laboratory fuel cell configuration. A 1 M methanolsolution was supplied to the anode side (1 ml/min) while the humidifiedair (150 ml/min) at 70° C. Commercial PtRu spray coated electrode wasmeasured in the same conditions as reference. The active metal loadingof all anodes was 70-80 μg/cm². FIGS. 18A-B presents the potential andpower vs. current density plots of the fuel cells at 70° C. underdynamic current load operation control. Pt@Sn and PtSn@Sn peak powervalues attained in these measurements were 19.0 mW/cm² and 35.7 mW/cm²,respectively, far higher than the value attained in the case ofreference PtRu electrode (9.5 mW/cm²).

These relatively high power values are attributed to the uniquecore-shell structure of the Pt@Sn and PtSn@Sn materials comprised ofthin layer of catalyst on the core Sn nano-structures.

Example 4 Electrocatalysts Comprising Palladium

Catalyst Synthesis by Electroless Process by Ethylene Glycol AssistedReduction

In exemplary procedures, standard electrodes were prepared byelectrodeposition of Sn from a solution of 18 mM SnCl₂/50 mM sodiumcitrate in water, on TORAY® TGPH-090 carbon paper (1 cm²) to form 3Dtree-shaped Sn high surface area nano-structures. The electrodes werethen immersed in 10 mM water and ethylene glycol-water solutions of thecatalysts precursors: K₂PtCl₄, PdCl₂, SnCl₂ and RuCl₃, of differentcompositions, for selected time spans. By applying this electrolessprocess, a thin catalyst layer is formed on the Sn nano-trees. It isimportant to note that the electroless process was performed immediatelyafter the electrodeposition process to minimize the Sn passivation inair.

Catalysts Characterization:

Electrodeposition and electrochemical measurements were performed usingBiologic VSP multichannel potentiostate and CHInstruments 700C and 760Celectrochemical workstations, in a three electrode electrochemical cellusing Pt mash as counter electrode and Ag/AgCl reference electrode.

The electrodes active material content was measured by dissolvingelectrode coating in aqua regia solution and measuring it utilizingVarian 710-ES ICP system. XRD measurements were carried out using aPAnalytical X-ray diffractometer (X′Pert PRO). FTIR measurements wereconducted using Bruker Vertex 70 spectrophotometer.

Results

Pd, PtSn, PdSn, PtRu and ternary PtPdRu and PtPdSn catalysts weresynthesized on pre-electrodeposited Sn electrodes by electrolessdisplacement method. The activity of the best selected catalysts(compared with Pt) towards MF oxidation is presented in FIG. 19.

The physical and chemical properties of the attained materials wereexplored. Firstly, the morphology and structure of the obtainedcatalysts were studied.

Without being bound by any particular theory, it is assumed that theexceptional electroactivity of the PtPdSn electrodes, shown in FIG. 19is attributed to dual mechanism. According to this mechanism, methylformate can undergo “direct oxidation” to CO at potentials as low as 50mV, while the other path involves “indirect oxidation” of adsorbed CO atpotentials higher than 0.7 V.

Finding that these reactions can co-exist on Pd while Pt facilitatesonly the indirect path. Therefore, it was decided to further investigateand optimize these electrodes incorporating the high activity of Pd atlow potentials (direct oxidation path) and that of Pt at high potentialsregion (indirect oxidation path). PtPd and PtPdSn catalysts weresynthesized and tested in MF and dimethyl ether (DME), solutions.

FIG. 20 shows XRD patterns of PtPd and PtPdSn catalysts prepared byelectroless deposition on Sn particles. Except of main Sn peaks at 20values of 31.01° (200), 32.89° (101), 44.16° (220) and 45.15° (211), andthe main Pt peaks at new peaks at 15.78°, 21.71°, 42.51°, 66.88°, and75.66° are assigned to Pt—Sn phases. A broad wave above 30° may indicateon the formation of Pt—Pd phases.

In order to study the effect of Pt—Pd alloying on the electroactivity ofthe catalysts towards MF and DME oxidation, PtPd/Sn catalysts withdifferent Pt to Pd stoichiometric ratio were synthesized and evaluatedelectrochemically. Since methanol and formic acid (FA) are intermediatesin the indirect oxidation path of MF (see FIG. 19), a complementaryanalysis of the reactivity of these catalysts was also done in formicacid (FA) and methanol (MeOH) solutions. The electrochemical parameterscompiled from these measurements are presented in Table 2 below.

FIGS. 21A-D show cyclic voltammetric curves of DME, MF, FA and MeOHfuels oxidation on selected catalysts electrodes. These results arenormalized to the weight of the total active noble metal (Pt+Pd) forcomparison. For clarification, the given Pt to Pd ratios mentioned inthese curves corresponds to the ratios of the precursors used in thesynthesis, whereas the actual atomic ratio on measured by ICP were0.8:1, 0.52:1 and 0.85:1, for the 1:1, 2:3 and 3:2, respectively.Although the 1:1 and 3:2 (Pt to Pd ratio in precursors) electrodes havealmost the same atomic ratio, the electroactivity of the later electrodeis far more active (156.7 and 1061 mC/mg active novel metal,respectively, for MF oxidation). This may be attributed to the formationof different phases with different active sites in each synthesis. It isassumed that the synergistic effect between Pt and Pd leads to anenhanced electroactivity compared to Pt electrodes (see FIG. 19) or thenew phase identified in the XRD is promoting the reactions. Sn alloyedwith Pt or Pd enhances the electroactivity of the catalyst toward MF, FAand MeOH oxidation. PtPdSn@Sn electrodes were prepared by controllingthe immersion time spans of the Sn electrode in the Pt and Pd saltsolution. Electrochemical measurements of these electrodes in MF, FA,MeOH and DME performed by CV are shown in FIGS. 22A-D and are listed inTable 2 further showing the measured electrochemical parameters ofcatalysts in study in different fuel solutions (ECSA, Ei—OnsetPotential, Ep—Peak Potential, Ap—Integrated oxidation charge).

TABLE 2 Methyl Formate Electrode ECSA Methanol A_(p), A_(p), Type m²/mgE_(i), V E_(i), V E_(p), V mC/mg E_(p), V mC/mg PtPd 1:1 16.87 0.0750.035 0.325/0.72 156.7 0.068 167.3 PtPd 1:4 15.98 0.100 0.0420.372/0.741 226.9 0.700 54.6 PtPd 2:3 47.09 0.125 0.037 0.347/0.77 11270.714 1030 Ptpd 3:2 23.25 0.100 0.035 0.352/0.75 1061 0.695 812.9 PtPdSn10 min 32.51 0.095 0.045 0.325/0.74 396.8 0.688 356.7 PtPdSn 15 min43.68 0.100 0.000 0.460/0.875 2228 0.805 1201 PtPdSn 30 min 14.04 0.1280.022 0.380/0.738 996 0.675 477.4 (for the corresponding electrodetypes) Fromic Acid Dimethyl Ether A_(p), A_(p), E_(i), V E_(p), V mC/mgE_(i), V E_(p), V mC/mg 0.0 0.325/0.742 287.2 0.02 0.330/0.740 230.20.045 0.307/0.756 625 0.015 0.361/0.745 1190 0.020 0.320/0.730 586.50.112 0.440/0.652 330.4 −0.04 0.460/0.890 2571 0.100 0.440/0.725 425.10.03 0.340/0.722 587.7 0.075 0.375/0.772 287.7

As demonstrated, regarding the effect of the exposure time on Pt andPtSn catalysts, shorter time spans of immersion result in incompletecoverage process and catalyst layer, whereas too long time lead toenhanced corrosion seen as loss of material as well as formation ofthick catalyst layer of lower utilization. In the case of PtPdSn, 15minutes process was found to be the optimum immersion time span to yieldthe most active electrodes (2228 mC/mg catalyst vs. 397 and 996 mC/mg at10 and 30 minutes, respectively, for MF oxidation).

Regarding the DME oxidation, it should be noted that the electroactivityof the PtPdSn/Sn catalysts is far higher than that of Pt electrodes (425and 288 mC/mg for 15 and 30 minutes PtPdSn electrodes vs. 46 mC/mg forPt), and is maintained through tens of cyclic voltammetry cycles.

Within the scope of this disclosure, it is a critical to identify theoxidation products formed at each potential. This approach may allow thedevelopment of new ways of analyzing the oxidation mechanism of DME andMF on the disclosed catalysts, by monitoring the formation ofintermediates and products during the oxidation process.

Catalyst Synthesis by Ethylene Glycol Assisted Reduction without Support

In additional exemplary procedures, an appropriate amount oftetrachloroplatinate, palladium chloride and tin chloride was dissolvedin ethylene glycol by sonication. The pH of solution was adjusted to 12by slowly adding NaOH dissolved in ethylene glycol. The resultant darkbrown solution was heated in oil bath at 80° C. for one hour and thenthe temperature increased to 180° C. and the solution was kept at thistemperature for 4 hours. Hydrochloric acid was added to neutralize thesolution and the precipitate was washed several times with acetone andwater. Finally, the catalyst was dried under vacuum at 80° C. for 4hours. 1 mg of the catalyst was dissolved in freshly prepared aqua regia(H₂SO₄, HCl) and molar ratios of elements were determined by InductiveCoupled Plasma Atomic Emission Spectroscopy (ICP-OES), as presented inTable 3.

TABLE 3 Sample No. Catalyst Precursor composition Final composition 1.(PtPd)₃Sn (3:3:2) 3:3:2 3:3:2 2. (PtPd)₃Sn (1:2:1) 1:2:1 1:2:1 3.(PtPd)₃Sn (2:1:1) 2:1:2 2:1:2

Catalyst Synthesis by Galvanic Displacement (Supported on Sn)

In additional exemplary procedures, PtPd@Sn and PtPdSn@Sn catalysts wereprepared by galvanic replacement of active metals on electrodepositedtin dendrites and commercial tin nanoparticles. Electro-deposition oftin was performed on TORAY® carbon paper (1 cm²). The solution forelectro-deposition was prepared by dissolving tri-sodium citrate (0.05M)and tin chloride (0.018M) in deionized water. Tin chloride solution (25ml) was purged with nitrogen and electro-deposition was performed byapplying constant potential of −3.0 V and total charge of 10 Coulombs.

After tin deposition, the electrodes were washed with deionized waterand acetone and were dried under nitrogen. The precursor solution forgalvanic displacement of PtPd, and PtPdSn was prepared by dissolving therelevant active metal salts in appropriate ration in ethylene glycol andwater at 4:1 (V:V) ratio containing 50 mM of H₂SO₄. The solution waspurged with nitrogen before electroless deposition. The attainedcatalysts were washed with deionized water, then with acetone and driedunder nitrogen. After electrochemical testing all of the electrodes weredissolved in aqua-media and diluted 100 times in deionized water forICP-OES analysis.

Catalyst Preparation by Galvanic Replacement on Commercial TinNanoparticle

In additional exemplary procedures, commercial tin nanoparticles weretreated with hydrofluoric acid (1.0M) to remove the oxide layer beforegalvanic replacement. The solution for galvanic replacement of Pt, PtPd,and PtPdSn was prepared by dissolving corresponding active metal salts(5 mM) and SnCl₂ (50 mM) in ethylene glycol and water at 4:1 (V:V) ratiocontaining 50 mM of hydrofluoric acid. The resultant catalyst was washedand dried as mentioned above.

Electrochemical Testing

Electrochemical testing was performed in three electrode cells in whichPt mesh counter electrode and Ag/AgCl (3M KCl) reference electrode wasused. 5 mg of catalyst (PtPdSn) and 20 uL of NAFION® (5% in ethanol)were dispersed in 0.5 ml isopropyl alcohol and 0.5 ml water. 40 ul ofcatalyst ink was coated on 1 cm² TORAY® Carbon Sheet. All theelectrochemical measurements were performed in 0.5 M sulfuric acidsaturated with DME (0.76 M) at room temperature, as summarized in Table4.

TABLE 4 Sample No Catalyst Support I_(p) E_(p) Pt:Pd 1. PtPdSn SnDendrites 150 mA/mg 0.75 V 1.2:1 2. PtPdSn Sn Dendrites  90 mA/mg 0.70 V0.68:1 3. PtPdSn Sn Dendrites 120 mA/mg 0.70 V 0.98:1 4. PtPd SnDendrites  25 mA/mg 0.60 V 1:1 5. PtPd Sn Dendrites  25 mA/mg 0.60 V 1:16. PtPd SnO₂  25 mA/mg 0.65 V 1:1 7. (PtPd)₃Sn Unsupported  90 mA/mg0.60 V 1:1 8. PtSn Unsupported 150 mA/mg 0.70 V PtSn (1:1) 9. PtCommercial 110 mA/mg 0.70 V PtSn (4:1) Tin NPs

Fabrication of Membrane Electrode Assembly for Fuel Cell

In additional exemplary procedures, anode catalyst ink (e.g., PtPdSn3:3:2) was prepared by dispersing catalyst in water with appropriateamount of Carbon Black and NAFION °. Similarly, cathode catalyst ink wasprepared by dispersing Pt black (JOHNSON MATTHEY™), carbon black(VULCAN™ XC72™), NAFION® and TEFLON® in appropriate amount of water. Thecatalyst ink was directly spray coated on membrane (the NAFION® 212) anddried under vacuum at 60° C. Catalyst coated membrane (MEA—membraneelectrode assembly) was soaked overnight in water to hydrate andlaboratory prototype single cell was assembled using TORAY® carbon assupport on anode side and carbon cloth on cathode side. The catalystloading on anode and cathode was 1.2 mg/cm² and 3.5 mg/cm²,respectively.

The electrodes were activated by flowing hydrogen on anode side andhumidified nitrogen on the cathode side. Both DME and compressed air waspassed through humidity bottle at a given temperature and directlysupplied as a gas. The DME and air flow rate was 40 ml/min and 400ml/min respectively.

Example 5 Electrocatalysts Comprising Lead Support

An example of methanol oxidation on Pt@Pb is shown in FIG. 23 presentingcyclic voltammetry of Pt@Pb in H₂SO₄ and methanol.

It can be concluded that such lead support catalysts are active in theoxidation of other fuels mentioned herein throughout.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

All publications, patents and patent applications mentioned in thisspecification are herein incorporated in their entirety by referenceinto the specification, to the same extent as if each individualpublication, patent or patent application was specifically andindividually indicated to be incorporated herein by reference. Inaddition, citation or identification of any reference in thisapplication shall not be construed as an admission that such referenceis available as prior art to the present invention. To the extent thatsection headings are used, they should not be construed as necessarilylimiting.

What is claimed is:
 1. A composition comprising: metal nanoparticles(NP) coated by a shell, wherein: said metal NPs comprise a metalselected from the group consisting of: tin (Sn), lead (Pb), antimony(Sb) or a combination thereof; said shell: (a) comprises a noble metal,and (b) is characterized by a thickness of less than 50 nm; and saidmetal is in an elemental state within said composition.
 2. Thecomposition of claim 1, wherein said element is Sn.
 3. The compositionof claim 1, wherein said thickness is in the range of 2 nm to 10 nm. 4.The composition of claim 1, wherein said noble metal is selected fromthe group consisting of: platinum (Pt), palladium (Pd), ruthenium (Ru),gold (Au), silver (Ag), rhodium (Rh), iridium (Ir), or an alloy or acombination thereof.
 5. The composition of claim 1, wherein said shellfurther comprises a metal selected from the group consisting of Sn, Pb,Sb, Mo, Co, Fe, Mn, Os, Ni, Ti, W, indium-tin-oxide and selenium (Se),including any oxide or a combination thereof.
 6. The composition ofclaim 1, wherein herein a median size of said metal nanoparticles isfrom 1 to 50 nanometers.
 7. The composition of claim 4, wherein said Pt,and Pd are in a molar ratio of from 3:1 to 1:3, respectively.
 8. Thecomposition of claim 1, wherein said composition is in a form of anelectrocatalyst configured for oxidation of a fuel.
 9. The compositionof claim 8, wherein said fuel is selected from the group consisting ofmethanol, ethanol, formic acid, formaldehyde, dimethyl ether, methylformate, and glucose.
 10. A fuel cell having an electrocatalystcomprising the composition of claim
 1. 11. The fuel cell of claim 10,wherein said electrocatalyst is anode.
 12. The fuel cell of claim 10,wherein said electrocatalyst is characterized by an electrochemicallyactive surface area of at least 30-75 m²g⁻¹.
 13. The fuel cell of claim10, wherein said electrocatalyst is electrocatalyst configured foroxidation of a fuel.
 14. The fuel cell of claim 13, wherein said fuel isselected from the group consisting of methanol, ethanol, formic acid,formaldehyde, dimethyl ether, methyl formate, ethylene glycol, propyleneglycol, and glucose.
 15. A process for manufacturing the composition ofclaim 1, comprising: (i) providing said metal NPs; and (ii) plating amaterial comprising said noble metal on said metal NPs, therebyobtaining said composition.
 16. The process of claim 15, wherein step(ii) is performed by electroplating or electroless plating, or by amethod selected from the group consisting of: chemical reduction,sputtering, chemical vapor deposition, ion beam enhanced deposition,plasma-assisted vapor deposition, cathodic arc deposition, ionimplantation and evaporation.
 17. The process of claim 15, wherein themetal is Sn.
 18. The process of claim 15, wherein step (ii) furthercomprises plating an additional metal on said metal NPs; wherein saidmetal is selected from the group consisting of: the group consisting ofSn, Pb, Sb, Mo, Co, Fe, Mn, Os, Ni, Ti, W, indium-tin-oxide and selenium(Se), including any oxide or a combination thereof.